[Bug target/46094] New: -fsplit-stack doesn't honour x86_64 ABI wrt. stack alignment

[Bug target/46094] New: -fsplit-stack doesn't honour x86_64 ABI wrt. stack alignment

[zsojka at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46094

           Summary: -fsplit-stack doesn't honour x86_64 ABI wrt. stack
                    alignment
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zsojka@seznam.cz


If I understand http://www.x86-64.org/documentation/abi.pdf correctly, and the
ABI described here is valid enough, -fsplit-stack doesn't align stack correctly
when calling functions.
At the moment of function entry, this should hold: (rsp&15)==8

As example, I will use the testcase from PR46093 (
http://gcc.gnu.org/bugzilla/attachment.cgi?id=22091 ). There are values of rsp
at the moment of function entry:

GDB breakpoints:
b main
b foo
b __morestack
b __morestack_block_signals
b __generic_morestack
b __morestack_unblock_signals
b __generic_releasestack
b pthread_sigmask
b sigprocmask

(for some reason, breakpoint at __morestack wasn't set correctly by this
procedure, so I had to set it manually)

function                    rsp
main                        0x7fffffffde58
__morestack                 0x7fffffffde50
__morestack_block_signals   0x7fffffffddf0
sigprocmask                 0x7fffffffddf0
__generic_morestack         0x7fffffffde00
__morestack_unblock_signals 0x7ffff7ff9ff8
sigprocmask                 0x7ffff7ff9ff8
foo                         0x7ffff7ff5fe8
...

this could cause problem if (for example) sigprocmask() used SSE instructions
to access stack